Method of manufacturing a semiconductor device and a process of a thin film transistor

ABSTRACT

To enable radiating an optimum energy beam depending upon the structure of a substrate (whether a metallic film is formed or not) when an amorphous semiconductor film is crystallized and uniformly crystallizing the overall film, first, a photoresist film and the area of an N +  doped amorphous silicon film on the photoresist film are selectively removed by a lift-off method. Hereby, the amorphous silicon film is thicker in an area except an area over a metallic film (a gate electrode) than in the area over the metallic film. In this state, a laser beam is radiated. The N +  doped amorphous silicon film and an amorphous silicon film are melted by radiating a laser beam and afterward, melted areas are crystallized by cooling them to room temperature. As the amorphous silicon film is thicker in the area except the area under which the metallic film (the gate electrode) is formed than in the area under which the metallic film is formed, the maximum temperature of the surface of the film is equal and the overall film can be uniformly crystallized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device in which a film is formed by crystallizing asemiconductor film by radiating an energy beam on the semiconductor filmsuch as amorphous silicon, particularly relates to a method ofmanufacturing a semiconductor device provided with structure in whichthe substrate material of a semiconductor film to be crystallized is noteven such as a thin film transistor (TFT) used for a liquid crystaldisplay (LCD) and others.

2. Description of the Related Art

A TFT liquid crystal display uses a thin film transistor (TFT) for apixel provided with a switching function and this TFT is formed on aglass substrate corresponding to each pixel of the liquid crystaldisplay. There are two types of TFTs of TFT consisting of amorphoussilicon films and TFT consisting of polycrystalline silicon films, andhigh-performance TFT consisting of polycrystalline silicon films ofthese can be produced on a glass substrate at low temperature byirradiating an amorphous silicon film with an energy beam, particularlyan excimer laser beam. The peripheral circuit of a liquid crystaldisplay and a pixel switching device can be produced on the samesubstrate by using such TFT consisting of polycrystalline silicon films.Recently, TFT provided with bottom gate structure attracts attention ofTFTs consisting of polycrystalline silicon films because particularly,stable characteristics can be obtained.

This TFT provided with bottom gate structure is constituted as shown inFIG. 9 for example. That is, a gate electrode 101 consisting ofmolybdenum tantalum (MoTa) is formed on a glass substrate 100 and anoxide film (Ta₂O₅) 102 is formed on this gate electrode 101. A gateinsulating film consisting of a silicon nitride (SiN_(x)) film 103 and asilicon dioxide (SiO₂) film 104 is formed on the glass substrate 100including this oxide film 102 and further, a thin polycrystallinesilicon film 105 is formed on this silicon dioxide film 104. A sourcearea 105 a and a drain area 105 b are respectively formed by dopingN-type impurities for example in this polycrystalline silicon film 105.A silicon dioxide film (SiO₂) 106 is selectively formed corresponding tothe channel area 105 c of this polycrystalline silicon film 105 on thepolycrystalline silicon film 105. An N⁺ doped polycrystalline siliconfilm 107 is formed on the polycrystalline silicon film 105 and thesilicon dioxide film 106 and further, a source electrode 108 and a drainelectrode 109 are respectively formed opposite to the source area 105 aand the drain area 105 b on this N⁺ doped polycrystalline silicon film107.

This TFT provided with bottom gate structure can be manufactured by thefollowing method: That is, after a molybdenum tantalum (MoTa) film isformed on an overall glass substrate 100, a gate electrode 101 is formedby patterning this molybdenum tantalum film by etching so that the filmis in a predetermined shape. Afterward, an oxide film 102 is formed onthe surface of the gate electrode 101 by anodizing the gate electrode101. Next, a silicon nitride film 103, a silicon dioxide film 104 and anamorphous silicon film are sequentially formed on the overall oxide film102 by plasma enhanced chemical vapor deposition (PECVD).

Next, this amorphous silicon film is once fused by irradiating thisamorphous silicon film with a laser beam by an excimer laser for exampleand afterward, crystallized by cooling the film to room temperature.Hereby, the amorphous silicon film is changed to a polycrystallinesilicon film 105. Next, after a silicon dioxide film 106 in the shapecorresponding to a channel area is selectively formed on thepolycrystalline silicon film 105 of a part to be a channel area, anamorphous silicon film including N-type impurities, for examplephosphorus (P) and arsenic (As) is formed and changed to an N⁺ dopedpolycrystalline silicon film 107 by irradiating the above amorphoussilicon film with a laser beam by an excimer laser again, and theimpurities are electrically activated.

Next, after an aluminum (Al) film is formed on the overall film by asputtering method using argon (Ar) as sputtering gas, this aluminum filmand the N⁺ doped polycrystalline silicon film 107 are respectivelypatterned by etching so that they are in a predetermined shape, and asource electrode 108 and a drain electrode 109 are respectively formedon a source area 105 a and a drain area 105 b. Next, dangling bond andothers are inactivated by exposing the above silicon dioxide film tohydrogen and hydrogenating a channel area 105 c by a hydrogen radicaland atomic hydrogen which both pass through the silicon dioxide film106. TFT provided with bottom gate structure shown in FIG. 9 can beobtained by the above process.

OBJECT AND SUMMARY OF THE INVENTION

As described above, in the prior method, an energy beam is radiated ontoan amorphous silicon film in a process for crystallizing it, however, atthis time, the structure of a substrate under the amorphous silicon filmis not even. That is, a metallic film (the gate electrode 101) isapplied on the glass substrate 100, the substrate under the amorphoussilicon film consists of metal and glass which are different in materialand heretofore, an energy beam is simultaneously radiated onto anamorphous silicon film over the respective substrate and film. In thiscase, the same energy beam as the following energy is also radiated ontoan amorphous silicon film over the glass substrate 100 based upon theoptimum condition of the crystallizing energy of the amorphous siliconfilm in a channel area over the metallic film (the gate electrode 101).

However, even if the same amorphous silicon film is used, the optimumvalue of energy required for crystallization is different depending uponwhether a substrate is made of metal or glass because thermalconductivity is different. Therefore, more energy beam is radiated ontothe amorphous silicon film on the glass substrate 100 by the priormethod according to the optimum condition of the amorphous silicon filmon the metallic film (the gate electrode 101) than the optimum conditionand therefore, there is a problem that partially a film is broken.

The present invention is made to solve such problems and the object isto provide a method of manufacturing a semiconductor device in which anoptimum quantity of energy beams can be radiated depending upon thestructure of a substrate when an amorphous semiconductor film iscrystallized, an overall film can be uniformly crystallized and a filmis never broken.

A method of manufacturing a semiconductor device according to thepresent invention comprises a process for selectively forming a metallicfilm on a substrate, a process for forming an amorphous semiconductorfilm on the substrate and the metallic film so that an area on thesubstrate is thicker than an area on the metallic film and a process foruniformly polycrystallizing the semiconductor film by radiating anenergy beam onto the semiconductor film.

More concretely, a method of manufacturing a semiconductor deviceaccording to the present invention comprises a process for forming ametallic film as the gate electrode of a thin film transistor on thesurface of a substrate and forming an insulating film on this metallicfilm and the substrate, a process for forming a first amorphoussemiconductor film the thickness of which is uniform on theinsulating-film, a process for selectively forming a lift-off film in anarea on the first semiconductor film corresponding to the metallic film,a process for forming a second amorphous semiconductor film thethickness of which is uniform including impurities on the lift-off filmand the first semiconductor film and a process for polycrystallizing thefirst and second semiconductor films by radiating an energy beam afterthe lift-off film and an area on the lift-off film of the secondsemiconductor film are selectively removed and respectively forming thesource area and the drain area of the thin film transistor.

A method of manufacturing a semiconductor device according to thepresent invention may be also constituted so that it comprises a processfor forming a metallic film as the gate electrode of a thin filmtransistor on the surface of a substrate and forming an insulating filmon this metallic film and the substrate, a process for selectivelyforming a lift-off film in an area on the insulating film correspondingto the metallic film, a process for forming a first amorphoussemiconductor film the thickness of which is uniform includingimpurities on the lift-off film and the insulating film, a process forforming a second amorphous semiconductor film the thickness of which isuniform on the insulating film and the first semiconductor film afterthe lift-off film and an area on the lift-off film of the firstsemiconductor film are selectively removed and a process forpolycrystallizing the first and second semiconductor films by radiatingan energy beam after the second semiconductor film is formed andrespectively forming the source area and the drain area of the thin filmtransistor.

According to a method of manufacturing a semiconductor device accordingto the present invention, as the thickness of a semiconductor film isdifferent depending upon the state of a substrate (whether a metallicfilm is formed or not) when an energy beam is radiated to crystallize anamorphous semiconductor film, the overall semiconductor film can beuniformly crystallized by radiating beams with the same energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to C are sectional views showing a method of manufacturing athin film transistor equivalent to a first embodiment according to thepresent invention every process;

FIGS. 2A and 2B are sectional views showing a process next to FIG. 1;

FIGS. 3A to 3D are sectional views showing a method of manufacturing athin film transistor equivalent to a second embodiment according to thepresent invention every process;

FIGS. 4A and 4B explain the basic principle of the present invention,FIG. 4A is a sectional view showing structure in which a metallic filmis formed under a silicon film and FIG. 4B is a sectional view showingstructure in which a metallic film is not formed under a silicon film;

FIG. 5 shows parameters of each material used for simulation forexplaining the principle shown in FIG. 4;

FIG. 6 is a drawing showing a characteristic for explaining the changeof the temperature of a silicon film when a laser beam is radiated onthe structure shown in FIG. 4A;

FIG. 7 is a drawing showing a characteristic for explaining the changeof the temperature of a silicon film when a laser beam is radiated onthe structure shown in FIG. 4B;

FIG. 8 is a drawing showing a characteristic showing the thickness of asilicon film in the structure shown in FIG. 4B to the thickness (30 nm)of an insulating film shown in FIG. 4A for obtaining the maximumtemperature of 2650 K in both structures shown in FIGS. 4A and 4B; and

FIG. 9 is a sectional view for explaining the prior structure of a thinfilm transistor and the manufacturing method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to drawings, embodiments according to the present inventionwill be described in detail below.

Prior to the concrete description of the embodiments, first, the basicprinciple of the present invention will be described. As describedabove, even if the same amorphous silicon film is used, the optimumvalue of energy required for crystallization is different depending uponwhether a substrate is made by metal or glass. According to the presentinvention; an overall semiconductor film can be uniformly crystallizedby radiating beams with the same energy by changing the thickness of theamorphous silicon film depending upon the structure of a substrate(whether a metallic film is formed or not). The reasons will bedescribed below.

FIGS. 4A and 4B show examples of substrates which are different in thesubstrate structure of a silicon film. The structure shown in FIG. 4A isformed by sequentially forming a nickel (Ni) film 41 on a glasssubstrate 40, a silicon nitride (SiN) film 42, an insulating film (SiO₂)43 and an amorphous silicon film (a-Si) 44 on the nickel film. In themeantime, the structure shown in FIG. 4B is formed by sequentiallyforming a silicon nitride (SiN) film 42 on a glass substrate 40, aninsulating film (SiO₂) 43 and an amorphous silicon film 44 and is thesame as the structure shown in FIG. 4A except that a metallic film (thenickel film 41) is not formed under the amorphous silicon film 44.

FIG. 6 shows the result of simulating the change of the temperature ofthe surface of the amorphous silicon film 44 when an excimer laser beam(energy: 360 mJ/cm², pulse length: 30 ns, wavelength: 308 nm) isradiated onto the amorphous silicon film 44 in the structure shown inFIG. 4A as an energy beam. In the meantime, FIG. 7 shows the result ofsimulating the change of the temperature of the surface of the amorphoussilicon film 44 when the same excimer laser beam is radiated onto theamorphous silicon film 44 in the structure shown in FIG. 4B. FIG. 5shows the parameters of the material of each film.

As clear from the result of FIGS. 6 and 7, while an excimer laser beamis radiated, the temperature of the amorphous silicon film 44 rapidlyrises to a melting point (the melting point of a-Si) and when thetemperature reaches the melting point, the incline of rising is oncegentle because of the latent heat of melting and afterward, thetemperature rapidly rises again. Even if excimer laser beams with thesame energy are radiated, the maximum temperature is different dependingupon the substrate structure of the amorphous silicon film 44. That is,if a metallic film (the nickel film 41) is formed below the amorphoussilicon film 44 as shown in FIG. 4A, the maximum temperature isapproximately 2650 (K), while if a metallic film (the nickel film 41) isnot formed below the amorphous silicon film as shown in FIG. 4B, themaximum temperature is approximately 2940 (K) and is greatly differentdepending upon the structure of a substrate. The difference between themaximum temperatures is increased as the insulating film 43 is thinned.When the radiation of an excimer laser beam is finished after thetemperature reaches the maximum temperature, heat is transmitted in thedirection of the glass substrate 40 and the temperature of the amorphoussilicon film 44 gradually falls in both structures shown in FIGS. 4A andB. When the temperature reaches temperature required for crystallizingsilicon (1410° C.), latent heat is generated by crystallization, thetemperature is held fixed for some time (crystallizing time) andafterward, gradually falls again.

If an excimer laser beam is radiated onto the amorphous silicon film 44in the respective structures shown in FIGS. 4A and B, it is desirable soas to optimize a laser beam condition that the maximum temperature whichcan be achieved by the same energy of the surface of each amorphoussilicon film 44 is the same. The inventors of the present inventionconsider that if a silicon film on a metallic film (the nickel film 41)is thickened in the structure shown in FIG. 4B, the same temperaturecondition as in the structure shown in FIG. 4A can be set and therefore,the temperature of the surface of the silicon film can be equalindependent of the structure of a substrate (whether a metallic film isformed or not) and obtain a drawing showing a characteristic in FIG. 8in experiments.

FIG. 8 shows the thickness of the silicon film 44 in the structure shownin FIG. 4B to that of the silicon film 44 which is 30 nm shown in FIG.4A for obtaining the maximum temperature of 2650 K in both structuresshown in FIGS. 4 A and B. That is, FIG. 8 shows the result of simulatingthe thickness of the silicon film 44 in the structure shown in FIG. 4Bin case that in the structure shown in FIG. 4A, the thickness of thesilicon film 44 on the nickel (Ni) film 41 is set to 30 nm, thethickness of the nickel film 41 is set to 100 nm, the thickness of thesilicon nitride (SiN) film 42 is set to 50 nm and the thickness of aninsulating film (SiO₂) 43 is changed so that the temperature of thesurface of the silicon film in the structures shown in FIGS. 4A and Breaches 2650 K (the boiling point of silicon). This result shows thatwhen the thickness of the insulating film 43 in the structure shown inFIG. 4A is reduced, the silicon film is required to be thickened in thestructure shown in FIG. 4B to obtain the same maximum temperature. Thatis, the result shows that the thickness of the silicon film in thestructure shown in FIG. 4B has only to be set according to the resultshown in FIG. 8 so that the maximum temperature of the surface of thesilicon film 44 obtained by radiating an energy beam in the structuresshown in FIGS. 4A and B can be equal so as to optimize a laser beamcondition.

The present invention utilizes such a result for uniformly crystallizingan overall film at the same maximum temperature by changing thethickness of a silicon film depending upon the structure of a substrate(whether a metallic film is formed or not) on the same substrate. Anexample in which the present invention is applied to a method ofmanufacturing a thin film transistor will be described below.

First Embodiment

FIGS. 1A to C and FIGS. 2A and B show a method of manufacturing a thinfilm transistor equivalent to a first embodiment of the presentinvention in the order of processes. First, as shown in FIG. 1A, a gateelectrode 11 consisting of a nickel (Ni) film the thickness of which is100 nm is formed on the overall surface of a substrate, for example aglass substrate 10 by sputtering using argon (Ar) as sputtering gas.Next, a laminated insulting film 12 is formed by sequentially forming asilicon nitride (SiN_(x)) layer which is 50 nm thick and a silicondioxide (SiO₂) layer which is 100 nm thick on the overall surfacesimilarly by sputtering using helium (He) as sputtering gas, and next,an amorphous silicon film 13 which is 30 nm thick is formed on theinsulating film 12 by PECVD for example.

After the amorphous silicon film 13 is formed, a photoresist is appliedonto this amorphous silicon film 13 and exposure (back exposure) 15 tothis photoresist by gamma rays (wavelength: 436 nm) for example isexecuted from the rear side of the glass substrate 10. At this time, aphotoresist film 14 with the same width as the gate electrode 12 asshown in FIG. 1B is formed by self-matching with the gate electrode 12functioning as a mask. Next, as shown in FIG. 1C, an N⁺ doped amorphoussilicon film 16 including N-type impurities, for example phosphorus (P)is formed on the insulating film 12 and the photoresist film 14 by PECVDfor example. The temperature of the substrate at this time shall be theheat-resistant temperature (for example, 150° C.) of the photoresist orless. The thickness of the N⁺ doped amorphous silicon film 16 isdetermined according to the result shown in FIG. 8 based upon thethickness of the SiO₂ layer of the insulating film 12. As the thicknessof the SiO₂ layer of the insulating film 12 is set to 100 nm in thisembodiment, the required thickness of the amorphous silicon film in anarea except the gate electrode 11 is 48 nm as shown in FIG. 8.Therefore, the thickness of the N⁺ doped amorphous silicon film 16 isset to 18 nm obtained by subtracting 30 nm (the thickness of theamorphous silicon film 13) from 48 nm.

Afterward, as shown in FIG. 2A, the photoresist film 14 and the area ofthe N⁺ doped amorphous silicon film 16 on the photoresist film 14 (thatis, an area corresponding to a channel area) are selectively removed bya lift-off method. Hereby, the amorphous silicon film is thicker in anarea except an area over metal (the gate electrode 11) than in the areaover the metal. In this state, next, a laser beam 17 is radiated fromthe surface of the substrate. The N⁺ doped amorphous silicon film 16 andthe amorphous silicon film 13 are melted by radiating a laser beam 17 asdescribed above and afterward, melted areas are crystallized by coolingthem to room temperature. At this time, the N-type impurities in the N⁺doped amorphous silicon film 16 are diffused on the side of theamorphous silicon film 13 and an N⁺ doped polycrystalline silicon film18 provided with a source area 18 a and a drain area 18 b is formed. Asin this embodiment, the amorphous silicon film is thicker in the areaexcept the area over the metallic film (the thickness of the amorphoussilicon film: 48 nm) than in the area over the metallic film (the gateelectrode 11) (thickness: 30 nm), the maximum temperature of the surfaceof the film is substantially equal as described above and the overallfilm can be uniformly crystallized.

It is desirable for a laser beam 17 that a laser beam the wavelength ofwhich the N⁺ doped amorphous silicon film 18 can absorb, particularly apulse laser beam by an excimer laser is used. In detail, a pulse laserbeam (wavelength: 308 nm) by XeCl excimer laser, a pulse laser beam(wavelength: 350 nm) by XeF excimer laser and others are used.

Next, as shown in FIG. 2B, electrodes 19 a and 19 b consisting ofaluminum (Al) are respectively formed on the source area 18 a and thedrain area 18 b in the N⁺ doped polycrystalline silicon film 18 bysputtering using argon (Ar) as sputtering gas. Next, the channel area 18c in the N⁺ doped polycrystalline silicon film 18 is hydrogenated inhydrogen plasma to inactivate dangling bond and others.

As described above, according to the method of manufacturing a thin filmtransistor equivalent to this embodiment, as the thickness of a siliconfilm is set to a different value depending upon the structure of asubstrate (whether a metallic film is formed or not) when a laser beam17 is radiated for crystallization, the silicon film can be uniformlycrystallized over the overall substrate. Therefore, a film is neverbroken and a process margin can be increased.

Second Embodiment

FIGS. 3A to 3D show a method of manufacturing a thin film transistorequivalent to a second embodiment of the present invention in the orderof processes. In this embodiment, the order in the first embodiment offorming an amorphous silicon film and a doped amorphous silicon film isinverted.

That is, first as shown in FIG. 3A, a gate electrode 31 consisting of anickel (Ni) film which is 100 nm thick is formed on the overall surfaceof a substrate, for example a glass substrate 30 by sputtering usingargon (Ar) as sputtering gas. Next, a laminated insulating film 32 whichis 100 nm thick is formed by sequentially forming a silicon nitride(SiN_(x)) film and a silicon dioxide (SiO₂) film on the overallsubstrate similarly by sputtering using helium (He) as sputtering gasand next, a photoresist is applied onto this insulating film 32 andexposure (back exposure) 35 to this photoresist by gamma rays(wavelength: 436 nm) for example is executed from the rear side of theglass substrate 30. At this time, a photoresist film 33 with the samewidth as the gate electrode 31 is formed by self-matching with the gateelectrode 31 functioning as a mask. Next, an N⁺ doped amorphous siliconfilm 34 including N-type impurities, for example phosphorus (P) isformed on the insulating film 32 and the photoresist film 33 by PECVDfor example. The temperature of the substrate at this time shall be theheat-resistant temperature (for example, 150° C.) of the photoresist orless. The thickness of this N⁺ doped amorphous silicon film 34 isdetermined according to a drawing showing a characteristic shown in FIG.8 based upon the thickness of the insulating film 32 as in the firstembodiment. That is, as the thickness of the SiO₂ layer of theinsulating film 32 is set to 100 nm in this embodiment, the requiredthickness of the amorphous silicon film in an area except the gateelectrode 31 is 48 nm as shown in FIG. 8. Therefore, the thickness ofthe N⁺ doped amorphous silicon film 34 is set to 18 nm obtained bysubtracting 30 nm (the thickness of anamorphous silicon film 36 to beformed continuously) from 48 nm.

Afterward, as shown in FIG. 3B, the photoresist film 33 and the area ofthe N⁺ doped amorphous silicon film 34 on the photoresist film 33 (thatis, an area corresponding to a channel area) are selectively removed bya lift-off method.

Next, as shown in FIG. 3C, an amorphous silicon film 36 which is 30 nmthick is formed on the N⁺ doped amorphous silicon film 34 and theinsulating film 32 by PECVD for example. Hereby, the amorphous siliconfilm is thicker in an area (the thickness of the amorphous silicon film:48 nm) except an area over metal (the gate electrode 31) than in thearea (thickness: 30 nm) over metal. In this state, next, a laser beam 37is radiated on the overall surface from the surface of the substrate.The N⁺ doped amorphous silicon film 34 and the amorphous silicon film 36are melted by radiating a laser beam 17 as described above andafterward, melted areas are crystallized by cooling them to roomtemperature. At this time, the N-type impurities in the N dopedamorphous silicon film 34 are diffused on the side of the amorphoussilicon film 36 and an N⁺ doped polycrystalline silicon film 38 providedwith a source area 38 a and a drain area 38 b is formed. As in thisembodiment, the amorphous silicon film is also thicker in the area (thethickness of the amorphous silicon film: 48 nm) except the area over themetallic film than in the area (thickness: 30 nm) over the metallic film(the gate electrode 31), the maximum temperature of the surface of thefilm is substantially equal and the overall film can be uniformlycrystallized.

Next, as shown in FIG. 3D, electrodes 39 a and 39 b consisting ofaluminum (Al) are respectively formed on the source area 38 a and thedrain area 38 b in the N⁺ doped polycrystalline silicon film 38 bysputtering using argon (Ar) as sputtering gas. Next, a channel area 38 cin the N⁺ doped polycrystalline silicon film 38 is hydrogenated inhydrogen plasma to inactivate dangling bond and others.

As described above, according to the method of manufacturing a thin filmtransistor equivalent to this embodiment, as the thickness of a siliconfilm is set to a different value depending upon the state of a substrate(whether a metallic film is formed or not) when a laser beam 37 isradiated for crystallization, the silicon film can be uniformlycrystallized over the overall substrate and a film can be prevented frombeing broken.

The embodiments according to the present invention are described above,however, the present invention is not limited to the above embodimentsand may be variously transformed. For example, in the above embodiments,a metallic film under a silicon film is a nickel film, however, it maybe also formed by the other metallic film. In the above embodiments, asilicon film is used for an amorphous semiconductor film, however, theother amorphous film may be also used if only it can be crystallized byradiating an energy beam. Further, in the above embodiments, the presentinvention is applied to a method of manufacturing a thin filmtransistor, however, it may be also applied to a process formanufacturing the other semiconductor device. A method of formingamorphous semiconductor films different in thickness depending upon thestructure of a substrate is not limited to the methods described in theabove embodiments and the other method may be also used.

As described above, according to the methods of manufacturing asemiconductor device according to the present invention, as thethickness of a semiconductor film is set toga different value dependingupon the state of a substrate (whether a metallic film is formed or not)when an energy beam is radiated to crystallize the amorphoussemiconductor film, the overall semiconductor film can be uniformlycrystallized by radiating beams with the same energy. Therefore, thereis effect that a film is never broken and a process margin can beincreased.

1-15. (canceled)
 16. A method of manufacturing a semiconductor device,comprising: forming a gate electrode on a portion of a top side of asubstrate, said gate electrode being a metallic film; forming aninsulating film on said substrate and said gate electrode; forming alift-off film on said insulating film wherein said lift-off film is aphotoresist; forming an N⁺ doped amorphous semiconductor film with auniform thickness on said photoresist and said insulating film whereinsaid uniform thickness of said N⁺ doped amorphous semiconductor film isa function of a thickness of said insulating film; irradiating saidphotoresist from a rear side of said substrate; removing saidphotoresist film and said N⁺ doped amorphous semiconductor film on saidphotoresist; forming an amorphous semiconductor film on said N⁺ dopedamorphous semiconductor film and said insulating film; irradiating saidamorphous semiconductor film and said N⁺ doped amorphous semiconductorfilm with an energy beam with a set optimum value of energy required forcrystallization; uniformly crystallizing said amorphous semiconductorfilm and a residual area of said N⁺ doped amorphous semiconductor filmby cooling them to room temperature, wherein a thickness of saidamorphous semiconductor film is thicker in an area over said metallicfilm than in an area not covering said metallic film, and a temperatureat a surface of said crystallized amorphous semiconductor film and saidN⁺ doped amorphous semiconductor film is substantially equal; andforming source and drain electrodes in predetermined positions on saidamorphous semiconductor film and said N⁺ doped amorphous semiconductorfilm.